Steel components of industrial and marine gas turbine engines are subjected in normal use to a variety of operating conditions, particularly in terms of the ambient atmosphere. In some situations the air drawn into the engine has constituents which are corrosive and abrasive to the compressor blades and other such parts in spite of their relatively high chromium content and generally corrosion resistant nature. It has been proposed, consequently, that a protective coating be provided against such corrosive attack and while various metallic coatings have been suggested and tried, none has qualified for technical or economic reasons. Ceramic coatings have also been proposed, but have not solved the problem because even the most rugged of them are chipped and broken in normal gas turbine engine operation, exposing the underlying steel surfaces to corrosive attack.